THE mother of a 22-month-old child was "severely sleep deprived" and suffering from so-called "forgotten baby syndrome" when her son was found dead in her car in 2015, the Coroner has been told.

Romy Zunde’s son Noah Zunde was found in a car outside a Kyneton childcare centre in February, 2015. The death is the subject of a coronial inquest.

Ms Zunde falsely believed she dropped her son at childcare that morning.

She returned in the afternoon to collect him, not realising he had been in the back seat the entire time, according to a medical expert's report given to the Victorian Coroners Court.

The report stated that in the week leading up to the death, Ms Zunde hadn't been able to sleep well due to suspected gastroenteritis. Initially she was unwell with vomiting and nausea and later her daughter fell sick too.

The night before the death, Noah was uncomfortable due to teething and slept in his parents bed, meaning Ms Zunde was virtually unable to sleep, according to police statements by Ms Zunde's partner, Andrew Krespanis.

On the morning of the death, Thursday February 19, Ms Zunde had to disrupt her usual morning routine to drop off a misplaced myki card to her partner at Kyneton train station so he could get to work, the report said.

Mr Kespanis described Ms Zunde as "considerably distressed" from the disruption and the possibility of her daughter being late for school.

Ms Zunde traveled to Tylden Primary School for the school drop off and then instead of taking her son Noah to Bambini Child Care Services, she traveled home and commenced doing chores, the report said.​

In her statement Ms Zunde said the childcare was "very close to ours, a left turn directly opposite the right turn to our house. I can only assume I automatically made a right turn instead of left".

Ms Zunde also didn't have the usual memory "cues" that Noah was in the car, according to expert neuroscientist associate professor Matthew Mundy, including the fact the baby seat was not visible from the driver's seat.

"Without a visual cue to the presence of Noah, it is less likely that Romy Zunde would have been reminded of his presence after a failure in short term memory of driving home instead of to Bambini daycare," the report said.

"Noah must have fallen asleep on the way.… he was probably asleep in the car which is something he hardly ever did," Ms Zunde stated in her interview with police.

"This seems important, since he would normally be making some kind of noise during the journey. Again, these observations would also suggest a lack of external 'cues' to prompt the maintenance of Romy's short-term memory".

​"Ms Zunde had suffered several days of acute sleep deprivation," Mundy submitted.

"She was overwhelmed with confusion and thought about several alternatives where she could have left Noah."

Associate Professor Mundy said Zunde's exhaustion had affected her long term, short term and habitual memory and led her to believe she had dropped Noah at the daycare centre close to their home.

The sleep deprivation was partly due to suspected gastroentritis of Zunde and her primary school age daughter, along with Noah’s teething discomfort.

Father Andrew Krespanis told police he and Ms Zunde resorted to having Noah in their bed, which was very uncomfortable for her and resulted in her getting "much if any sleep".

"Noah had a really - almost unprecedented night of not sleeping" Ms Zunde told police adding she "needed help" due to her fatigue but could not ask for it.

The report also found that Ms Zunde said to a woman at her daughter's primary school that morning that it had been a "hellish" week. The witness said Ms Zunde was "very fatigued" and "probably overwhelmed".

Sleep is required for memories to be consolidated so the deprivation would have decreased the likelihood that Ms Zunde remembered her child was in the car, the report said.

Mundy also stated that a recent change to the childcare routine adding an extra day meant Ms Zunde's habitual memory took over and led to an error.

Ms Zunde told police she had been on "auto pilot" during the trip from her daughter's school that afternoon.

She said "the change in routine...the extra care on Thursday and (her daughter) starting school...Over the school holidays (her daughter) and Noah doing childcare days together...dropping them off together," added to her belief she had dropped Noah at daycare.

"In my opinion, it is possible that due to the recently changed routine for the destination of a Thursday drive (which would otherwise have been to the family home), and the competing and confusing information from the other items held in long term memory (arrangements for Fridays, arrangements for previous weeks etc.), there was a potential for error introduced into the day's travel," it said.

Mundy submitted that Ms Zunde's memory may have been affected by stressful situations including a recent dog attack on the family's pet pigs as well having to retrieve a forgotten Myki pass that morning so her partner could travel to work.